Pull type harvesting machines are towed from the tractor by a hitch arm which requires to be adjusted in angle relative to the frame of the machine for fine steering movements and more coarse movement to the transport position.
Some machines are required to follow the tractor only to one side and thus include a hitch arm which is located at one end of the machine. In others in which the present invention is particularly effective, the hitch arm to the tractor extends from the frame over the header to a hitch coupling and can be swung by an operating cylinder from one side of the header to the other so that the header can be located in echelon with the tractor to one side and symmetrically to the other side.
Pull-type harvesting machines of this type are well known and there are many different examples manufactured by a number of different companies.
The pull type harvesting machines that are mechanically driven use a coupling which attaches the hitch arm to the tractor together with a mechanical linkage which connects to the power take off shaft of the tractor to communicate the driving power from the PTO shaft to the mechanically driven elements of the header.
Disc headers which utilize as the cutting system a plurality of spaced discs across the width of the header with each disc rotating about a respective vertical axis are known and widely used. In view of the relatively high power consumption of disc headers, it is often desirable to communicate the drive hydraulically. A drive with a high power requirement is not typically better suited to be hydraulic. In fact it would often be better suited for the drive to be mechanical, as hydraulic drive would generally result in poorer drive transmission efficiencies than mechanical systems. However the hydraulic drive system generally offers more accurate control of input torque, less maintenance of the system, and fewer moving parts.
Thus a pump is provided adjacent the forward end of the hitch arm which attaches to the power take off shaft of the tractor. The pump generates a flow of high pressure hydraulic fluid which passes through a hydraulic line from the pump along the hitch arm to a motor at the cutter system. A return line runs from the motor back to a filter and from the filter into a sump tank which is commonly provided as the hollow interior of the tubular hitch arm.
A simple construction provides a mechanical connection of the forward end of the hitch arm to the draw bar of the tractor so that the hitch arm is directly attached to the draw bar of the tractor. In a simple construction commonly the pump is simply a separate item which attaches to the PTO shaft and is supported thereby. This arrangement is adequate for lower powered systems where the weight of the pump is relatively low so that it avoids applying significant loading to the PTO shaft which could cause damage.
However in higher power systems, it is desirable that the pump is mounted on the hitch construction so that it is properly supported from the draw bar with little or no loads being transferred to the PTO shaft.
One example of an arrangement of this type is shown in U.S. Pat. No. 4,838,358 (Freudendahl) issued Jun. 13, 1989. This discloses an arrangement of this type which attaches the forward end of the hitch arm to a tractor either to a draw bar or to the lower arms of the three point hitch and also attaches the pump to the tractor in a manner which supports the pump from the draw bar or the hitch rather than from the PTO shaft.
This arrangement has however a number of disadvantages in that different designs are provided for the draw bar construction and for the three-point hitch construction and of course it is highly desirable that a common design is provided. Furthermore the arrangement locates the pump at a forward position which reduces the length of the connecting shaft which can be connected between the pump and the PTO shaft which thus reduces manoeuverability.
In addition this arrangement provides no attention to the requirement for cooling of the hydraulic system particularly when high power transfer is required since high power of course generates a high level of heat in the pump and the motor.
Another arrangement is disclosed in U.S. Pat. No. 6,625,964 (McLeod) issued Sep. 30, 2003. This construction provides a complex device for towing equipment in a row one behind the other which has achieved no commercial success.